OCing is best for gaming. If you are doing it for any reason then do it for that reason.
OCing the processor, especially the 2500k, is definitely worth doing if you are the type. However, it will likely be good enough without it. The video card is generally the easier and more effective thing to OC, though, if you want increased gaming performance.
Corsair has the highest RAM failure rates, I would choose Crucial or Kingston instead (the two with the lowest).
The PSU will be fine, but OCZ is just of lower quality than a similar wattage XFX brand (Seasonic OEM) PSU.
Asus Z68 boards also have higher failure rates than Gigabyte. You might want to switch it out for a similar board from Gigabyte instead for about the same price.
Also, you may want to save up a bit more and go with a different case instead. The case you are using has a big impact on how long your computer lasts before things start breaking. Improved airflow keeps everything cooler and cooler means it will last longer.
They are also durable, you can use the same case for the next 5 computers, so you can amortize the cost of it over 20 years and even a good case only costs like $5 a year.
You make up the whole cost the first time something breaks from heat failure (like your $200+ video card.
The Antec 300 (and/or 300 Illusion) and the HAF 912 are both really good entry level cases for people serious about proper cooling.
and go to the RAM maker's website and look for motherboard support list
That would be harder since Amazon.co.uk doesn't throw the part numbers at you like most good websites do. You will have to use some internet search time figuring out the part number, and then look that up on the maker's website and look for the motherboard support list.
You would be fine if either the right pairing is present on either list. It doesn't have to be on both at once.
- Edit - If you want to save yourself some effort, you can just buy RAM with this part number and it will work CT2KIT51264BA1339